Lab 12: Cerebellum

Question 1

Input via the inferior cerebellar peduncle

Answer 1

• vestibular receptors
• body surface and muscle receptors
• inferior olivary nucleus

Question 2

Input via the middle cerebellar peduncles

Answer 2

• widespread areas of the cerebral cortex, after a synapse in pontine nuclei
• Outflow reaches the upper motor neuron systems via the superior cerebellar peduncle

Question 3

Outflow via the Superior Cerebellar Peduncle

Answer 3

• Cerebral cortex, especially the SMA, after a synapse in the thalamus
• the red nucleus

Question 4

Outflow via the Inferior Cerebellar Peduncle

Answer 4

-fibers from the cerebellum travel to brainstem upper motor neurons (vestibular nuclei, reticular nuclei)

Question 5

Overview of the Intrinsic connections of the Cerebellum

Answer 5

axons that enter the cerebellum as climbing fibers from inferior olivary nuclei or mossy fibers from all other input terminate in the:

• cerebellar cortex
• deep nuclei of the cerebellum

Impulse transmission within the cerebellar cortex includes:

• termination of climbing fibers on Purkinje cell dendrites and deep cerebellar nuclei
• termination of mossy fibers on granule cells and deep nuclei
• ascent of granule cell axons as parallel fibers in the molecular layer
• termination of parallel fibers on Purkinje cells
• descent of Purkinje cell axons to deep cerebellar nuclei

Question 6

Gross Anatomy of the Cerebellum

Answer 6

• major regions: vermis (midline region) and hemispheres (lateral)
• foldings of cerebellar cortex: folia (elevations like gyri) and fissures (depressions like sulci)

Question 7

Anterior Lobe of the cerebellum

Answer 7

• anterior to primary fissure

- hard to find except on sagittal surface

Question 8

Posterior lobe of the cerebellum

Answer 8

Most of cerebellum posterior to the primary fissure
-includes:
Tonsil: part of the cerebellar hemisphere that extends close to the midline; can herniated through the foramen magnum as a result of increased intracranial pressure

Question 9

Flocculonodular Lobe of the Cerebellum

Answer 9

Nodule (nodules): vermal part

Flocculus: hemispheric part; found laterally, near the VIIth and VIIIth cranial nerves and the lateral aperture or foramen of Luschka, indicated grossly by the presence of choroid plexus

Question 10

Gross connections of the cerebellum with the brainstem

Answer 10

Superior cerebellar peduncle: cerebellum to midbrain

Middle Cerebellar peduncle: cerebellum to pons

Inferior cerebellar peduncle: cerebellum to medulla

Question 11

VestibuloCerebellum

Answer 11

Flocculonodular lobe; important for balance and eye movements

Question 12

Spinocerebellum

Answer 12

Vermis (median zone) and medial hemisphere (intermediate zone)
-important fort adjustments for smooth movement of proximal (median zone) and distal limb (paramedian zone)

Question 13

Cerebrocerebellum

Answer 13

-lateral hemisphere or zone: involved in motor planning

Question 14

Fastigial Nucleus

Answer 14

Adjacent to midline; receives fibers from vestibulocerebellum and vermis of the spinocerebellum

Question 15

Interposed Nuclei

Answer 15

-receive fibers from the paramedian zone of the spinocerebellum

Question 16

Dentate Nucleus

Answer 16

-most lateral, largest, wrinkled; receives fibers from the cerebrocerebellum

Question 17

Molecular Layer

Answer 17

-contains stellate and basket cell bodies

Question 18

Purkinje Layer

Answer 18

Contains single row of Purkinje cell bodies

Question 19

Granule Cell Layer

Answer 19

Contains granule cell bodies

Question 20

Input/Output of the Cerebellum via Inferior Cerebellar Peduncle

Answer 20

• vestibulonuclei: receives fibers from the fastigial nucleus and cortex of the vestibulocerebellum. Send fibers to the vestibulocerebellar cortex and fastigial nucleus (as do axons directly from the vestibular nerve). Influences LMNs via vestibulospinal tracts and vestibulo-ocular paths
• receptors: both deep (esp. muscle spindles) and superficial-send impulses via fibers that pass through the lateral area of the spinal cord and the brainstem to enter the cerebellum via the inferior cerebellar peduncle
• Inferior olivary nucleus: receive input from cerebral cortex, reticular formation and red nucleus. Send climbing (olivocerebellar) fibers to the contralateral cerebellum via the inferior cerebellar peduncle
• Reticular Formation: contains reticular nuclei that receive drivers from the fastigial nucleus and influence LMNs via the reticulospinal tract

Question 21

Input to the cerebellum via the middle cerebellar peduncle

Answer 21

basis pedunculi (crus cerebri) of midbrain contains:

• corticopontine fibers: medial 2/5 and lateral 2/5 of peduncle; are fibers from the cerebral cortex en route to synapse on pontine nuclei of the basal pons. Pontine nuclei send fibers across the midline into the contralateral middle cerebellar peduncle.
• corticospinal and corticobulbar fibers: middle 1/5 of basis pedunculi

Middle cerebellar peduncle: a major INPUT system to the cerebellum from the cerebral cortex, after a synapse in the pontine nuclei; contains only pontocerebellar fibers

• pontine nuclei: a pale group of cells in the base of the pons that are involved in transmission of info from the cerebral cortex to the cerebellum. They: receive terminals of corticopontine fibers and send mossy fibers to the contralateral cerebellar cortex and deep nuclei via middle cerebellar peduncle
• pontocerebellar fibers: leave pontine nuclei and cross midline to enter the contralateral middle cerebellar peduncle and travel to the cerebellar cortex and deep nuclei

Question 22

Outflow from cerebellum via superior cerebellar peduncle

Answer 22

Contain fibers from interposed and dentate nuclei of the cerebellum that travel to and terminate in the red nucleus as cerebellorubral fibers and the thalamus as cerebellothalamic fibers

Question 23

Levels of the Superior Cerebellar Peduncle

Answer 23

Rostral pons: located medial to the lateral lemniscus

Pons/midbrain transition: the beginning of the decussation of the superior cerebellar peduncle

Caudal Midbrain: the decussation of the superior cerebellar peduncle

NOTE: the lateral lemniscus is peripheral to the superior cerebellar peduncles in the rostral pons and terminates in the inferior colliculus. At the level of the inferior colliculus and caudal midbrain, the superior cerebellar peduncles travel centrally and decussate and are covered laterally by the general sensory paths (ALS, medial lemniscus, VTTT)

Question 24

Red Nucleus

Answer 24

-receive cerebellorubral fibers from contralateral cerebellum; magnocellular part receives fibers from interposed nuclei and forms the rubrospinal tract

Question 25

Cerebellothalamic Fibers

Answer 25

-fibers from the dentate and interposed nuclei that travel lateral to the red nucleus en route to ventral lateral nucleus (VL) of thalamus

From the thalamus, fibers ascend in the posterior limb of the internal capsule to reach primary motor and premotor cortices

Question 26

Clinical Tests for Cerebellum

Answer 26

1. Walking a straight line (a test for Gait ataxia)
2. Heel-to-shin test (a test for lower limb ataxia in the absence of antigravity function)
3. Finger to nose test (a test for a synergy of movement and intention tremor)
4. Rapid alternating movements (to show dysdiadochokinesia)
5. Stretch reflex (to show hypotonia)
6. Have eyeballs follow finger (to test for eyeball oscillation or nystagmus)